U.S. patent number 7,607,607 [Application Number 12/108,488] was granted by the patent office on 2009-10-27 for de-rotation system suitable for use with a shaft fairing system.
This patent grant is currently assigned to Sikorsky Aircraft Corporation. Invention is credited to Frank P. D'Anna, David A. Darrow, Jr., Thomas L. Sbabo.
United States Patent |
7,607,607 |
Darrow, Jr. , et
al. |
October 27, 2009 |
**Please see images for:
( Certificate of Correction ) ** |
De-rotation system suitable for use with a shaft fairing system
Abstract
A de-rotation system includes a first ring gear defined about an
axis of rotation, a second ring gear defined about the axis of
rotation and a gear set in meshing engagement with the first ring
gear and the second ring gear to control a position of a housing
about the axis of rotation.
Inventors: |
Darrow, Jr.; David A.
(Stratford, CT), D'Anna; Frank P. (Seymour, CT), Sbabo;
Thomas L. (Hamden, CT) |
Assignee: |
Sikorsky Aircraft Corporation
(Stratford, CT)
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Family
ID: |
40507071 |
Appl.
No.: |
12/108,488 |
Filed: |
April 23, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090084891 A1 |
Apr 2, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11432875 |
May 12, 2006 |
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60693592 |
Jun 24, 2005 |
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60684694 |
May 26, 2005 |
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60776278 |
Feb 23, 2006 |
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Current U.S.
Class: |
244/17.19;
244/130; 114/243; 416/41; 416/33; 416/244R; 416/179; 416/124;
244/17.27; 244/17.23 |
Current CPC
Class: |
B64C
27/14 (20130101); B64C 7/00 (20130101); B64C
27/10 (20130101); B64C 27/12 (20130101); B64C
27/20 (20130101); B64C 27/04 (20130101) |
Current International
Class: |
B64C
27/00 (20060101) |
Field of
Search: |
;244/17.19,17.23,17.27,130 ;416/33,41,124,179,244R ;114/243 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Title: Summary of Rotor Hub Drag Data; By: G.N. Keys and H.J.
Rosenstein; Dated: Mar. 1978. cited by other .
Title: Experimental Investigation of Advanced Hub and Pylon Fairing
Configurations to Reduce Helicopter Drag; By: D.M. Martin, R.W.
Mort, L.A. Young, P.K. Squires; Dated: Sep. 1993, NASA Technical
Memorandum 4540. cited by other .
Title: The First 50 Years Were Fine . . . But What Should We Do for
an Encore?--The 1994 Alexander A. Nikolsky Lecture; By: Evan A.
Fradenburgh; Journal of the American Helicopter Society; Jan. 1995.
cited by other .
Title: Rotorcraft Hub Shroud; By: LTC Chip Lunn; Brannon
Industries; Apr. 11, 2006. cited by other .
PCT International Search Report and written opinion mailed Aug. 19,
2008 for PCT/US06/20349. cited by other.
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Primary Examiner: Eldred; J. Woodrow
Attorney, Agent or Firm: Carlson, Gaskey & Olds PC
Parent Case Text
The present application is a Continuation-In-Part of U.S. patent
application Ser. No. 11/432,875, filed May 12, 2006, which claims
priority to U.S. Provisional Patent Application Nos. 60/693,592,
filed Jun. 24, 2005; 60/684,694, filed May 26, 2005; and
60/776,278, filed Feb. 23, 2006.
Claims
What is claimed is:
1. A de-rotation system for a fairing comprising: a first ring gear
rotatable about a rotor axis of rotation; a second ring gear
rotatable about said rotor axis of rotation; a gear set in meshing
engagement with said first ring gear and said second ring gear; a
housing which supports said gear set, said gear set operable to
control a position of said housing about said rotor axis of
rotation; and a shaft fairing mounted to said housing for rotation
about said rotor axis of rotation.
2. The system as recited in claim 1, wherein said gear set is
operable to control an azimuthal position of said housing such that
said fairing remains in an approximately fixed azimuthal
position.
3. The system as recited in claim 1, wherein said shaft fairing is
airfoil shaped.
4. The system as recited in claim 1, wherein said first ring gear
and said second ring counter-rotate.
5. The system as recited in claim 1, wherein said gear set
comprises a first pinion in meshing engagement with an inner
diameter of said first ring gear and a second pinion in meshing
engagement with an outer diameter of said second ring gear, said
first pinion gear rotationally mounted to said second pinion gear
through a pinion shaft.
6. The system as recited in claim 1, wherein said gear set
comprises a first chain in engagement with said first ring gear and
a second chain in engagement with said second ring gear.
7. The system as recited in claim 6, further comprising an upper
gear set in meshing engagement with said upper chain, a lower gear
set in meshing engagement with said lower chain and an idler gear
set therebetween.
8. The system as recited in claim 6, further comprising: a first
shaft rotatable about a first axis of rotation displaced from said
rotor axis of rotation; a first driven gear mounted to said first
shaft, said first driven gear in meshing engagement with said first
chain; a first idler gear mounted to said first shaft; a first
sprocket arm; a first idler sprocket mounted to said first sprocket
arm, said first idler sprocket in meshing engagement with said
second chain, said first idler sprocket rotatable about a first
sprocket axis displaced from said first axis; a second shaft
rotatable about a second axis of rotation; a second driven gear
mounted to said second shaft, said second driven gear in meshing
engagement with said second chain; a second idler gear mounted to
said second shaft, said second idler gear in meshing engagement
with said first idler gear; a second sprocket arm; a second idler
sprocket mounted to said second sprocket arm, said second idler
sprocket in meshing engagement with said first chain, said second
idler sprocket rotatable about a second sprocket axis displaced
from said second axis.
9. The system as recited in claim 7, further comprising a clutch
system mounted to said first shaft to selectively disengage said
gear set to permit said shaft fairing to rotate freely about said
axis of rotation.
10. The system as recited in claim 1, wherein said gear set further
comprising an upper gear set in meshing engagement with said first
ring gear, a lower gear set in meshing engagement with said second
ring gear and an idler gear set therebetween.
11. The system as recited in claim 1, wherein said gear set
comprises a first driven gear in engagement with said first ring
gear and a second driven gear in engagement with said second ring
gear.
12. The system as recited in claim 11, wherein said first driven
gear and said second driven gear cooperate through an idler gear
set.
13. The system as recited in claim 12, wherein said idler gear set
include a multitude of gears on a first shaft rotatable about a
first shaft axis and a multiple of gears on a second shaft
rotatable about a second shaft axis, said first shaft axis parallel
to said second shaft axis.
14. The system as recited in claim 12, wherein said idler gear set
include a multitude of gears on a first shaft and a multiple of
gears on a second shaft, said first shaft driven by said first
driven gear and said second shaft driven by said second driven
gear.
15. A counter-rotating coaxial rotor system comprising: a lower
rotor hub mounted to a lower rotor shaft which rotates about a
rotor axis of rotation; an upper rotor hub mounted to an upper
rotor shaft which rotates about said rotor axis of rotation in a
direction counter to said rotation of said lower rotor shaft, said
upper rotor shaft mounted at least partially through said lower
rotor shaft; an upper hub fairing mounted at least partially about
said upper rotor hub; a lower hub fairing mounted at least
partially about said lower rotor hub; a shaft fairing mounted
between said upper hub fairing and said lower hub fairing for
rotation about said rotor axis of rotation; a first ring gear
defined about said rotor axis of rotation, said first ring gear
mounted for rotation with said upper rotor shaft; a second ring
gear defined about said rotor axis of rotation, said first ring
gear mounted for rotation with said lower rotor shaft; a gear set
in meshing engagement with said first ring gear and said second
ring gear; and a housing mounted to said shaft fairing to support
said gear set, said gear set operable to control a position of said
shaft fairing about said axis of rotation.
16. The system as recited in claim 15, wherein said gear set
comprises a first pinion in meshing engagement with an inner
diameter of said first ring gear and a second pinion in meshing
engagement with an outer diameter of said second ring gear, said
first pinion gear rotationally mounted to said second pinion gear
through a pinion shaft.
17. The system as recited in claim 15, further comprising: a first
chain in engagement with said first ring gear; a second chain in
engagement with said second ring gear; a first shaft rotatable
about a first axis of rotation; a first driven gear mounted to said
first shaft, said first driven gear in meshing engagement with said
first chain; a first idler gear mounted to said first shaft; a
first sprocket arm; a first idler sprocket mounted to said first
sprocket arm, said first idler sprocket in meshing engagement with
said second chain, said first idler sprocket rotatable about a
first sprocket axis displaced from said first axis; a second shaft
rotatable about a second axis of rotation; a second driven gear
mounted to said second shaft said second driven gear in meshing
engagement with said second chain; a second idler gear mounted to
said second shaft, said second idler gear in meshing engagement
with said first idler gear; a second sprocket arm; a second idler
sprocket mounted to said second sprocket arm, said second idler
sprocket in meshing engagement with said first chain, said second
idler sprocket rotatable about a second sprocket axis displaced
from said second axis.
18. The system as recited in claim 15, wherein said gear set
further comprises: a first shaft rotatable about a first axis of
rotation; a first driven gear mounted to said first shaft, said
first driven gear in meshing engagement with said first ring gear;
a first idler gear mounted to said first shaft; a second shaft
rotatable about a second axis of rotation; a second driven gear
mounted to said second shaft, said second driven gear in meshing
engagement with said second ring gear; a second idler gear mounted
to said second shaft, said second idler gear in meshing engagement
with said first idler gear.
19. An aircraft having a counter-rotating coaxial rotor system
comprising: a lower rotor hub mounted to a lower rotor shaft which
rotates about a rotor axis of rotation; an upper rotor hub mounted
to an upper rotor shaft which rotates about said rotor axis of
rotation in a direction counter to said rotation of said lower
rotor shaft, said upper rotor shaft mounted at least partially
through said lower rotor shaft; an upper hub fairing mounted at
least partially about said upper rotor hub; a lower hub fairing
mounted at least partially about said lower rotor hub; a shaft
fairing mounted between said upper hub fairing and said lower hub
fairing for rotation about said rotor axis of rotation; a first
ring gear defined about said rotor axis of rotation, said first
ring gear mounted for rotation with said upper rotor shaft; a
second ring gear defined about said rotor axis of rotation, said
first ring gear mounted for rotation with said lower rotor shaft; a
gear set in meshing engagement with said first ring gear and said
second ring gear; and a housing mounted to said shaft fairing to
support said gear set, said gear set operable to control a position
of said shaft fairing about said axis of rotation.
20. The aircraft as recited in claim 19, wherein said aircraft is a
rotary-wing aircraft with a translational thrust system.
Description
BACKGROUND
The present invention is directed to a de-rotation system that
stabilizes a shaft fairing mounted between an upper hub fairing and
a lower hub fairing.
Typically, the aerodynamic drag associated with a rotor hub on a
rotary wing aircraft is a significant portion of the overall
aircraft drag, typically 25% to 30% for conventional single-rotor
helicopters. The rotor system drag increases for a rotary wing
aircraft having a counter-rotating, coaxial rotor system primarily
due to the dual rotor hubs and the interconnecting shaft
therebetween. For high-speed rotary wing aircraft, the increased
drag resulting from the counter-rotating, coaxial rotor system may
result in a relatively significant power penalty.
The aerodynamic drag of the dual counter-rotating, coaxial rotor
system is generated by three main components--the upper rotor hub
assembly, the lower rotor hub assembly, and the interconnecting
main rotor shaft assembly. The drag contribution may be
approximately 40% for each of the hubs, and 20% for the
interconnecting main rotor shaft assembly. Typically, a rotor hub
fairing arrangement is mounted to each of the upper rotor hub and
the lower rotor hub such that overall drag on the rotorcraft is
reduced. The interconnecting main rotor shaft between the upper
rotor hub assembly and the lower rotor hub assembly, however, is
typically exposed.
For a variety of reasons including, but not limited to, reduced
drag and low observability, shaft fairings have been developed to
cover the exposed interconnecting main rotor shaft. The shaft
fairing is mounted to the counter-rotating, coaxial rotor system
within a rotational environment between the upper hub fairing and
the lower hub fairing through a bearing arrangement.
During some flight conditions, the shaft fairing may undesirably
rotate relative the airframe which may increase drag and reduce the
low-observability benefits of the shaft fairing.
SUMMARY
A de-rotation system for a fairing according to an exemplary aspect
of the present invention includes: a first ring gear rotatable
about a rotor axis of rotation; a second ring gear rotatable about
the rotor axis of rotation; a gear set in meshing engagement with
the first ring gear and the second ring gear; a housing which
supports the gear set, the gear set operable to control a position
of the housing about the rotor axis of rotation; and a shaft
fairing mounted to the housing for rotation about the rotor axis of
rotation.
BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of this invention will become
apparent to those skilled in the art from the following detailed
description of the currently preferred embodiment. The drawings
that accompany the detailed description can be briefly described as
follows:
FIG. 1A is a general schematic view of an exemplary rotary wing
aircraft embodiment for use with the present invention;
FIG. 1B is general perspective view of a counter-rotating coaxial
rotor system mounting a rotor hub fairing system;
FIG. 1C is an expanded partial phantom view of a counter-rotating
coaxial rotor system mounting a rotor hub fairing system according
to one non-limiting embodiment of the present invention;
FIG. 2A is a perspective partial phantom view of a counter-rotating
coaxial rotor system illustrating a de-rotation system contained
within a shaft fairing;
FIG. 2B is an expanded view of the de-rotation system illustrated
in FIG. 2A;
FIG. 2C is a frontal view of the de-rotation system of FIG. 2A
taken through the rotor system axis of rotation;
FIG. 3 is a perspective view of another de-rotation system
according to another non-limiting embodiment;
FIG. 4 is a schematic view of another de-rotation system according
to another non-limiting embodiment;
FIG. 5A is a perspective view of a rotor system for use with a
de-rotation system mounted between an upper rotor system and a
lower rotor system;
FIG. 5B is a perspective view of the rotor system with an upper hub
fairing and a lower hub fairing mounted thereto;
FIG. 5C is an exploded view of the rotor system with a trailing
edge portion of a shaft fairing prior to assembly;
FIG. 5D is an exploded view of the rotor system with the trailing
edge portion of the shaft fairing positioned for receipt of a
leading edge portion of the shaft fairing; and
FIG. 5E is a perspective view of the rotor system with the rotor
hub fairing system mounted thereto.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
FIG. 1A illustrates an exemplary vertical takeoff and landing
(VTOL) rotary-wing aircraft 10 having a dual, counter-rotating,
coaxial rotor system 12 which rotates about an axis of rotation A.
FIG. 1B is general perspective of the counter-rotating coaxial
rotor system 12 mounting a rotor hub fairing system 36. The
aircraft 10 includes an airframe 14 which supports the dual,
counter rotating, coaxial rotor system 12 as well as an optional
translational thrust system 30 which provides translational thrust
generally parallel to an aircraft longitudinal axis L. Although a
particular aircraft configuration is illustrated in the disclosed
embodiment, other counter-rotating, coaxial rotor systems will also
benefit from the present invention.
The dual, counter-rotating, coaxial rotor system 12 includes an
upper rotor system 16 and a lower rotor system 18. Each rotor
system 16, 18 includes a plurality of rotor blades 20 mounted to a
rotor hub 22, 24 for rotation about the axis of rotation A. A
plurality of the main rotor blades 20 project substantially
radially outward from the hub assemblies 22, 24. Any number of
blades 20 may be used with the rotor system 12.
A main gearbox 26 which may be located above the aircraft cabin 28
drives the rotor system 12. The translational thrust system 30 may
be driven by the same main gearbox 26 which drives the rotor system
12. The main gearbox 26 is driven by one or more engines
(illustrated schematically at E). The gearbox 26 may be interposed
between the gas turbine engines E, the rotor system 12 and the
translational thrust system 30.
The translational thrust system 30 may be mounted to the rear of
the airframe 14 with a rotational axis T oriented substantially
horizontal and parallel to the aircraft longitudinal axis L to
provide thrust for high-speed flight. The translational thrust
system 30 in the illustrated non-limiting embodiment of FIG. 1A
includes a pusher propeller 32 mounted within an aerodynamic
cowling 34. Although a tail mounted translational thrust system 30
is disclosed in this illustrated non-limiting embodiment of FIG.
1A, it should be understood that any such system or other
translational thrust systems, including tractor and pod mounted
systems, may alternatively or additionally be utilized.
The rotor system 12 includes a rotor hub fairing system 36
generally located between and around the upper and lower rotor
systems 16, 18 such that the rotor hubs 22, 24 are at least
partially contained therein. The rotor hub fairing system 36
provides significant drag reduction with which large-scale flow
separation is greatly reduced.
The rotor hub fairing system 36 generally includes an upper hub
fairing 38, a lower hub fairing 40 and a shaft fairing 42
therebetween (also illustrated in FIG. 1B). The rotor hub fairing
system 36 is integrated such that the shaft fairing 42 generally
follows the contours of the upper hub fairing 38 and the lower hub
fairing 40 at the rotational interfaces therebetween to reduce
interference effects between the separate fairings 38, 40, 42 and
minimize flow separation in the junction areas. Furthermore, the
lower hub fairing 40 is integrated with the airframe 14 in an area
typically referred to on a rotorcraft as a pylon 14D (see FIG. 1C).
It should be understood that fairing systems of various
configurations will be usable with the present invention.
Referring to FIG. 1C, the shaft fairing 42 may be mounted to the
counter-rotating, coaxial rotor system 12 through a bearing
arrangement 43U, 43L (illustrated schematically) such that the
shaft fairing 42 may be positioned at a relative azimuthal position
about the axis of rotation A relative the airframe 14 by a
de-rotation system 44. The upper bearing arrangement 43U and the
lower bearing arrangement 43L may be respectively located adjacent
an upper portion and a lower portion of the shaft fairing 42. The
upper bearing arrangement 43U may be attached to one rotor shaft
12U, here the inner main rotor shaft 12U which drives the upper
rotor hub 22, while the lower bearing arrangement 43L is attached
to the other rotor shaft 12L, here the outer main rotor shaft 12L
which drives the lower rotor hub 24, such that the bearing
arrangement 43U, 43L are counter rotating and the net bearing drag
is relatively low. It should be understood that other shaft
arrangements may also be utilized herewith.
The de-rotation system 44 controls the position of the shaft
fairing 42 about the axis of rotation A such that the shaft fairing
42 remains in an essentially fixed azimuthal position relative the
airframe 14 irrespective of the flight regime and irrespective of
potential unequal parasitic friction of the bearing arrangement
43U, 43L. Although the present invention is described in connection
with a particular aircraft embodiment, it should be readily
appreciated that other areas which require an azimuthally
stationary fairing in a rotational environment will also benefit
herefrom.
Referring to FIG. 2A, the de-rotation system 44A includes a gear
system 46. The gear system 46 generally includes a first ring gear
48, a second ring gear 50, a gear set 52, and a housing 54. The
first ring gear 48 is mounted for rotation with the inner main
rotor shaft 12U and the second ring gear 50 is mounted for rotation
with the outer main rotor shaft 12L (also illustrated in FIG. 2B).
The first ring gear 48 includes an inner diameter gear 48G while
the second ring gear 50 includes an outer diameter gear 50G.
The housing 54 may be defined about axis A and surround the outer
main rotor shaft 12L. The housing may further be assembled from a
multiple of sections to facilitate maintenance or such like. The
housing 54 is mounted to the shaft fairing 42 and the main rotor
system 12 through the bearing arrangement 43U, 43L (also
illustrated in FIG. 2C) such that the shaft fairing 42 rotates with
the housing 54 about the axis of rotation A. The upper bearing
arrangement 43U and the lower bearing arrangement 43L maybe
respectively located adjacent an upper portion and a lower portion
of the housing 54. The upper bearing arrangement 43U is attached to
one rotor shaft 12U while the lower housing bearing 43L is attached
to the other rotor shaft 12L such that the bearings counter rotate
and the net bearing drag is relatively low.
The housing 54 includes a fitting 55 that supports the gear set 52.
The gear set 52 includes an upper pinion gear 56A, a lower pinion
gear 56B and a shaft 58 that rotationally connects the upper pinion
gear 56A and the lower pinion gear 56B. The upper pinion gear 56A
is in meshing engagement with the inner diameter gear 48G of the
first ring gear 48 and the lower pinion gear 56B is in meshing
engagement with the outer diameter gear 50G of the second ring gear
50.
The gear set 52 may be located in a forward section of the fairing
42 such that the de-rotation system 44A readily accommodates shaft
fairing geometries that exhibit a "necking", or "hour-glass" shape
(FIG. 2C). That is, the de-rotation system 44A is accomplished with
a low profile housing 54, relatively few parts and few gear meshes
to facilitate the "necking", or "hour-glass" fairing shape.
In operation, the first ring gear 48 rotates with the inner main
rotor shaft 12U in a first direction and the second ring gear 50
rotates with the outer main rotor shaft 12L in an opposite
direction to drive respective pinion gears 56A, 56B. The pinion
gears 56A, 56B rotate in the same direction due to the inner
diameter gear 48G of the first ring gear 48 and the outer diameter
gear 50G of the second ring gear 50. Rotation of the pinion gear
set 52 maintains the housing 54 and thus the shaft fairing 42 in a
stable rotational position relative the airframe 14.
Referring to FIG. 3, another non-limiting embodiment of a
de-rotation system 44B includes a gear set 60 to control the
position of the shaft fairing 42 about the axis of rotation A such
that the shaft fairing 42 remains in an essentially fixed azimuthal
position relative the airframe 14 irrespective of the flight
regimes and irrespective of potential unequal parasitic friction of
the bearing arrangement 43U, 43L.
A first chain 62U and a second chain 62L are driven in equal but
opposite directions about the axis of rotation A. The first chain
62U rotates with the rotor shaft 12U as the first chain 62U is in
engagement with a first ring gear 64U fixed for rotation with rotor
shaft 12U. The second chain 62L rotates with the rotor shaft 12L as
the second chain 62L is in engagement with a second ring gear 64L
fixed for rotation with rotor shaft 12L. It should be understood
that the although the term "chain" is utilized herein, other
members such as toothed belts, flex gears and the such like may
also be utilized.
The gear set 60 is mounted within a fitting 66 of a housing 68,
similar to what was described above for fitting 55 and housing 54.
The housing 68 is mounted to the shaft fairing 42 and the main
rotor system 12 through the bearing arrangement 43U, 43L such that
the housing 50 rotates with the shaft fairing 42 about the axis of
rotation A. The upper bearing arrangement 43U is attached to one
rotor shaft 12U while the lower housing bearing 43L is attached to
the other rotor shaft 12L such that the bearings counter-rotate and
the net bearing drag is relatively low.
The gear set 60 generally includes an upper gear set 70 driven
through the first chain 62U, a lower gear set 72 driven through the
second chain 62L and an idler gear set 74 therebetween. The gear
set 60 further includes a first shaft 76 which rotates about a
first axis of rotation G1 and a second shaft 78 which rotates about
a second axis of rotation G2. The shafts may be supported upon
respective shaft bearing arrangements 80, 82 which are mounted to
the fitting 66.
Shaft 76 supports a driven gear 84A and an idler gear 86A. A
sprocket arm 88A is mounted to the fitting 66 to support an idler
sprocket 90A which rotates about sprocket axis S1. The sprocket arm
88A facilitates an adjustable displacement between axis G1 sprocket
axis S1. The sprocket arm 88A may be manually adjustable to control
a tension within the first chain 62U. Alternatively, or in addition
thereto, the sprocket arm 88A may be spring biased to control the
tension. Shaft 78 supports a driven gear 84B and an idler gear 86B.
A sprocket arm 88B is mounted to the fitting 66 to support an idler
sprocket 90B which rotates about sprocket axis S2. The sprocket arm
88B facilitates adjustable displacement between axis G2 and
sprocket axis S2, similar to what was described above for the axis
G1 and sprocket axis S1.
The first chain 62U is engaged with the driven gear 84A and the
idler sprocket 90B. The second chain 62L is engaged with the driven
gear 84B and the idler sprocket 90A. That is, the shafts 76, 78
support the gears in essentially reverse order along their
respective axes G1, G2. The first chain 62U is in engagement with
the respective driven gear 84A and idler sprocket 90B while the
second chain 62L is in engagement with the respective driven gear
84B and idler sprocket 90A. The idler gears 86A, 86B are in direct
meshed engagement with each other to control the azimuthal position
of the housing 68 and the mounted shaft fairing 42. One of the
shafts 76, 78 and associated driven gear 84A, 84B--here illustrated
as shaft 78 and driven gear 84B--may further include a clutch
system 92 which selectively disengages the de-rotation system 44B
such that the shaft fairing 42 is free to rotate with, for example,
the relative wind. In other words, the driven gear 84B is not
driven due to the clutch system 92. Driven gear 84B no longer
drives driven idler gear 86B such that the idler gear set 74
essentially freewheels and the shaft fairing 42 is thereby no
longer driven such that the azimuthal position of the housing 68
and the mounted shaft fairing 42 is no longer controlled. This
essentially allows the shaft fairing 42 to be free to rotate about
the axis of rotation A, with, for example, the relative wind.
In operation, the first ring gear 64U rotates with the inner main
rotor shaft 12U in a first direction and the second ring gear 64L
rotates with the outer main rotor shaft 12L in a direction opposite
the first direction to drive respective chains 62U, 62L. The first
chain 62U drives the driven gear 84A and the idler sprocket 90B
while the second chain 62L drives the driven gear 84B and the idler
sprocket 90A while the idler gears 86A, 86B are in direct meshed
engagement with each other to maintain the fitting 66 of the
housing 68 and thus the shaft fairing 42 in a stable rotational
position relative the airframe 14.
Referring to FIG. 4, another non-limiting embodiment of a
de-rotation system 44C includes a gear set 100 to control the
position of the shaft fairing 42 about the axis of rotation A such
that the shaft fairing 42 remains in an essentially fixed azimuthal
position relative the airframe 14 irrespective of the flight
regimes and irrespective of potential unequal parasitic friction of
the bearing arrangement 43U, 43L.
The gear set 100 is mounted within a fitting 102 of a housing 104,
which(?) is mounted to the shaft fairing 42 or the main rotor
system 12 (FIGS. 5A-5E). The gear set 100 generally includes an
upper gear set 106U driven by the first ring gear 108, a lower gear
set 106L driven through the second ring gear 110 and an idler gear
set 112 therebetween. The first ring gear 108 is fixed for rotation
with rotor shaft 12U and the second ring gear 110 is fixed for
rotation with rotor shaft 12L. The gear set 100 further includes a
first shaft 114 which rotates about a first axis of rotation G1 and
a second shaft 116 which rotates about a second axis of rotation
G2. The shafts 114, 116 may be supported upon respective shaft
bearing arrangements 118, 120 which are mounted within the fitting
102.
Shaft 114 supports a driven gear 122A and an idler gear set 124A
while shaft 116 supports a driven gear 122B and an idler gear set
124B. The idler gear sets 124A, 124B may be manufactured of a
non-metallic material and may be a set that includes a multiple of
gears to accommodate the torque between shafts 114, 116.
The first ring gear 108 is in meshed engagement with the driven
gear 122A and the second ring gear 110 is in meshed engagement with
the driven gear 122B. The idler gears 124A, 124B are in direct
meshed engagement with each other to control the position of the
housing 104 and the mounted shaft fairing 42. One of the shafts
114, 116 and associated driven gear 122A, 122B--here illustrated as
shaft 114--may further include a clutch system 126 which
selectively disengages the de-rotation system 44B.
In operation, the first ring gear 108 rotates with the inner main
rotor shaft 12U in a first direction and the second ring gear 110
rotates with the outer main rotor shaft 12L in an opposite
direction to drive the respective driven gears 122A, 122B and
shafts 114, 116. The shafts 114, 116 counter-rotate in response to
the idler gear sets 124A, 124B being in meshed engagement to
maintain the housing 104 and thus the shaft fairing 42 in a stable
azimuthal position relative the airframe 14.
The de-rotation system 44A-44C is a passive system within which
derives its mechanical input from the main rotor system 12. The
power required is minimal as friction is the only opposing force
and gear meshes are noted as efficient power transfer mechanisms.
Since matching rotational speed is satisfied by the gear geometry
reduction ratio, the de-rotation system 44A will maintain a stable
azimuthal position alignment, regardless of main rotor RPM
variations.
It should be understood that relative positional terms such as
"forward," "aft," "upper," "lower," "above," "below," and the like
are with reference to an illustrated attitude of the structure and
should not be considered otherwise limiting.
Although particular step sequences are shown, described, and
claimed, it should be understood that steps may be performed in any
order, separated or combined unless otherwise indicated and will
still benefit from the present invention.
The foregoing description is exemplary rather than defined by the
limitations within. Many modifications and variations of the
present invention are possible in light of the above teachings. The
preferred embodiments of this invention have been disclosed,
however, one of ordinary skill in the art would recognize that
certain modifications would come within the scope of this
invention. It is, therefore, to be understood that within the scope
of the appended claims, the invention may be practiced otherwise
than as specifically described. For that reason the following
claims should be studied to determine the true scope and content of
this invention.
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